1. Field of the Invention
The present invention relates to an optical lens system, and more particularly, to a compact optical lens system used in electronic products for infrared band or visible light band.
2. Description of the Prior Art
In recent years, the application of imaging lens systems is getting wider and wider, especially in computer webcams, automotive lens assemblies, surveillance cameras, and electronic game devices. Generally, the sensor of a general photographing camera is none other than CCD (Charge Coupled Device) or CMOS device (Complementary Metal Oxide Semiconductor device). Along with the advances in semiconductor manufacturing technology, the pixel size of sensors is reduced leading compact imaging lens systems to higher resolution. In the meantime, the demand for better image quality is also increased.
A conventional imaging lens system with high resolving power, such as the one set forth in U.S. Pat. No. 7,365,920, generally has a front stop and four lens elements; wherein, the first and second lens elements are adhered together to form a doublet for correcting the chromatic aberration. However, this kind of arrangement has the following disadvantages. First, the degree of freedom in arranging the lens system is curtailed due to the employment of excessive number of spherical glass lenses; thus, the total track length of the system cannot be reduced easily. Second, the process of adhering glass lenses together is complicated, posing difficulties in manufacturing.
Besides, although the four-lens system disclosed in U.S. Pat. No. 7,848,032 does not have the aforesaid disadvantages, the system fails to be well-designed for infrared band. In considering the current situation that applications of lens systems capable in detecting infrared ray are getting more and more, the conventional four-lens systems designed only for visible light can no longer satisfy the current demands in the field.
In light of foregoing, there is a need for a compact lens system with excellent image quality and sensing susceptibility for portable electronic products, which can be applied not only in visible light band, but also in detecting infrared ray at night or circumstance of insufficient light source for catching high quality infrared image.